Have you found a workaround to the 'select input method' in the notification tray?

IT does...yes. But, once you CHOOSE it...it should go away.
But, you choose, it comes back..you choose, it comes back.
It's like 50 First Dates. lol
LOL. Kind of like the time - I look at it but it's still there, I look at it again but it's still there! Really, that keyboard icon is supposed to be there when any keyboard is open (assuming you have more than one) so you can switch keyboards easily anytime you want.
 
I kind of like having it there because it is a feature that makes it easier to switch between using 2 different keyboards without having to go back into the settings menu. I use Thumb Keyboard (it has a programmable shortcut key feature that I like to use for one touch insertion of my long gmail ID and some passwords and other long word or phrase entries) and the Google Keyboard (for swipe typing of text) and frequently switch between them. If you find notifications annoying, you can use a 3rd party launcher that allows you to hide the notification bar.
 
...interestingly enough this has started this week on my Note 3 using Swype not Swiftkey so we can see where the finger begins to point
 
I don't think there is a way around it. I haven't downloaded Swype or Swiftkey, I just use HTC's version, Trace Keyboard, which works pretty well. On the HTC One whenever I type the keyboard does appear on the notification bar. So maybe Android did intend for this to happen, to be a shortcut for those who switch between the keyboards.
 
It is there so you can switch between keyboards while typing in same message. Say you have an EMOJI keyboard and want to put in one, just quicky switch and there you go. It is not a problem, not really intrusive. Not like it pops up and says choose or die. Just roll with it. When you put the keyboard away, it goes away too.
 
Settings>Language & Input>then uncheck "Selector notification"...is what I did on mine...
 
I have a galaxy note 4 and I solved the problem with mine constantly asking me to select input method. I am using the Samsung keyboard and once I started tapping on the back key on bottom right on my phone which closes out the keyboard, it no longer comes up on my notifications status bar. I hope this helps! !